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Area Forecast Discussion (AFD)

Issued by Eureka, CA (EKA)

FXUS66 KEKA 231108

National Weather Service Eureka CA
408 AM PDT Fri Aug 23 2019

.SYNOPSIS...A gradual warming trend is expected today through the
middle of next week, with triple digit heat expected across many 
interior valley areas expected by Monday. Coastal areas are also 
expected to see above normal temperatures, again especially early 
next week. Little to no precipitation is expected. 


.DISCUSSION...Aside from limited patches near the Klamath and Eel
River Deltas, marine stratus clouds are largely absent from the 
North Coast as of 4 A.M. Friday. This is a significant departure 
from the prior morning, when widespread low stratus, fog, and 
even some drizzle lingered well into the late morning. The root 
cause is likely the rapid warming of temperatures in the lower 
atmosphere, which is clearly being observed by the atmospheric 
profiler at the Arcata/Eureka airport. While stratus south of the 
Bay Area does appear to be expanding and gradually spreading 
northward, and high resolution models do indicate that at least 
some redeveloping stratus is possible during the day, it seems 
most likely that coastal areas will remain largely clear of clouds
and fog for most of the daylight hours Friday. However, a 
gradually expanding ribbon of southerly flow along the immediate 
coast will likely bring stratus back into some coastal areas late 
this evening, at least as far north as Cape Mendocino, followed by
a reinforcing and expansive stratus shield from the west early 
Saturday morning. Shallow stratus and fog will then likely follow 
a typical pattern of moving inland overnight and lingering into 
the morning hours before diminishing during the afternoon Saturday
and possibly Sunday, before gradually eroding Monday and Tuesday.
Sunny skies will continue across interior areas through at least 

Meanwhile, gradually building high pressure aloft throughout the 
state is expected to drive a gradual warming trend today through 
Wednesday, with the peak of the heat expected Monday through 
Wednesday. Afternoon interior valley temperatures are expected to 
climb from the mid to upper 90s Friday through Sunday, to between 
100 and 105 degrees Monday through Wednesday...and perhaps locally
higher in a few of the warmer valleys. As a result, the threat of
light to moderate heat related impacts appears possible, 
particularly Monday through Wednesday. The bulk of the heat 
impacts are likely to be experienced across interior valley 
locations during the afternoons, particularly in Trinity County, 
but even coastal areas are likely to observe above normal 
temperatures by early next week. Still, low humidity and clear 
skies will promote radiational cooling and cool air drainage in 
interior valleys, and low temperatures are likely to fall into the
low 60s and even upper 50s overnight as a result. This will help
to mitigate heat impacts locally, but perhaps not quite as well in
areas to our east and northeast in the Central Valley and southern

Between Tuesday and Thursday, a weak upper level impulse is 
expected to move through the region from the southwest. This wave 
will likely drive lower surface pressure and light southerly winds
across the waters. While it's possible that this could eventually
result in another surge of very shallow marine stratus from the 
south, this will also likely lead to above normal coastal 
temperatures Monday through Wednesday. Meanwhile, while 
atmospheric moisture content appears to be meager, a small 
potential for isolated and mostly dry thunderstorms will continue 
to be monitored toward the middle of the week. /BRC


.AVIATION...Offshore flow has kept the coast mostly clear this 
morning with only a few local patches of stratus as of 3:30 AM. It
is possible the coastal airports could briefly be impacted around
sunrise, but this is looking less likely as the night progresses.
Confidence is high that there will remain clear through the 
afternoon today. Northerly winds of 10 to 15 kt are possible this 
afternoon along the coast with light winds inland.

Tonight winds at the coast are expected to turn southerly. This 
could bring some stratus north to at least Cape Mendocino and it may 
continue north Saturday morning. This will need to be monitored as 
it gets closer. MKK


.MARINE...Northerly winds continue across much of the area this 
morning, although some areas very near the coast are seeing 
southerly winds. The winds have diminished slightly over the waters 
and the gale warning set to expire at 5am looks on track. Seas will 
also slowly diminish today and tonight. Will likely need to issue a 
hazardous seas warning for the northern outer waters once the gale 

Tonight seas in the outer waters are expected to drop below 10 feet. 
For the weekend  and into Monday winds and short period seas will 
remain moderate to fresh. This will keep the steep seas around 7 to 
10 feet and small craft advisories will likely be needed. Closer to 
the coast local areas of southerly winds are expected. Most of these 
will be around 5 to 10 kt, but a few local areas of 10 kt are 
possible. These may not be captured in the coastal waters forecast, 
but will continue to highlight them in the discussion.

A west to northwest swell around 3 feet at 12 seconds continues to 
move through the waters. This is expected to continue through the 

Early next week winds will continue to diminish, although models are 
now keeping northerlies in the outer waters through Monday. By mid-
week models are trying to show a trough or upper level low moving 
into the area. The models are fairly confident that winds will be 
light, but are struggling with the position of the low and the 
direction of the surface winds. MKK


.FIRE WEATHER...A gradual warming trend is expected to unfold
throughout the region between today and Wednesday, with the peak 
of the heat expected between Monday and Wednesday. Inland 
afternoon high temperatures are likely to climb from the mid to 
upper 90s late in the week and over the weekend, to between 100 
and 105 degrees Monday through Wednesday. In addition to the 
increasing heat, humidity will also decrease, with low afternoon 
minimums expected and moderate to poor recoveries. Winds are not 
expected to be particularly strong on a large scale, and will be 
driven by typical daytime onshore and nighttime offshore 
fluctuations. Winds may become locally gusty on a smaller scale, 
most likely in areas where the terrain favors stronger upslope and
upvalley wind development. 

Meanwhile, little to no precipitation is expected for the 
foreseeable future. However, while it remains unlikely in 
northwest California, a very low chance for isolated dry 
thunderstorms near the middle of next week is being monitored. 


NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 5 PM PDT Saturday for PZZ450-455.

     Gale Warning until 5 AM PDT early this morning for PZZ470.

     Hazardous Seas Warning until 10 PM PDT this evening for PZZ475.



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